Hydrology Outweighs Temperature in Driving Production and Export of Dissolved Carbon in a Snowy Mountain Catchment

Journal Article · 20 July 2024 · Water Resources Research

DOI: https://doi.org/10.1029/2023WR036077 · OSTI ID:2407137

Kerins, Devon  ^[1]; Sadayappan, Kayalvizhi  ^[1]; Zhi, Wei  ^[1]; Sullivan, Pamela L.  ^[2]; Williams, Kenneth H.  ^[3]; Carroll, Rosemary W. H.  ^[4]; Barnard, Holly R.  ^[5]; Sprenger, Matthias  ^[6]; Dong, Wenming  ^[6]; Perdrial, Julia  ^[7]; Li, Li  ^[1]

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1. Department of Civil and Environmental Engineering The Pennsylvania State University University Park PA USA
2. College of Earth Ocean and Atmospheric Sciences Oregon State University Corvallis OR USA
3. Lawrence Berkeley National Laboratory Berkeley CA USA, Rocky Mountain Biological Laboratory Gothic CO USA
4. Desert Research Institute Reno NV USA
5. Department of Geography Institute of Arctic and Alpine Research University of Colorado Boulder CO USA
6. Lawrence Berkeley National Laboratory Berkeley CA USA
7. Department of Geology University of Vermont Burlington VT USA

Abstract Terrestrial production and export of dissolved organic and inorganic carbon (DOC and DIC) to streams depends on water flow and biogeochemical processes in and beneath soils. Yet, understanding of these processes in a rapidly changing climate is limited. Using the watershed‐scale reactive‐transport model BioRT‐HBV and stream data from a snow‐dominated catchment in the Rockies, we show deeper groundwater flow averaged about 20% of annual discharge, rising to ∼35% in drier years. DOC and DIC production and export peaked during snowmelt and wet years, driven more by hydrology than temperature. DOC was primarily produced in shallow soils (1.94 ± 1.45 gC/m ² /year), stored via sorption, and flushed out during snowmelt. Some DOC was recharged to and further consumed in the deeper subsurface via respiration (−0.27 ± 0.02 gC/m ² /year), therefore reducing concentrations in deeper groundwater and stream DOC concentrations at low discharge. Consequently, DOC was primarily exported from the shallow zone (1.62 ± 0.96 gC/m ² /year, compared to 0.12 ± 0.02 gC/m ² /year from the deeper zone). DIC was produced in both zones but at higher rates in shallow soils (1.34 ± 1.00 gC/m ² /year) than in the deep subsurface (0.36 ± 0.02 gC/m ² /year). Deep respiration elevated DIC concentrations in the deep zone and stream DIC concentrations at low discharge. In other words, deep respiration is responsible for the commonly‐observed increasing DOC concentrations (flushing) and decreasing DIC concentrations (dilution) with increasing discharge.  DIC export from the shallow zone was ~66% of annual export but can drop to ∼53% in drier years. Numerical experiments suggest lower carbon production and export in a warmer, drier future, and a higher proportion from deeper flow and respiration processes. These results underscore the often‐overlooked but growing importance of deeper processes in a warming climate.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0020146
• OSTI ID: 2407137
• Journal Information: Water Resources Research, Journal Name: Water Resources Research Journal Issue: 7 Vol. 60; ISSN 0043-1397
• Publisher: American Geophysical Union (AGU)Copyright Statement
• Country of Publication: United States
• Language: English